The linux installer has the softmod installation files on it, which is why it is much larger than the other. The splinter cell save is simply used to set the game into the emergency linux mode thingy. So all you have to do is start with a clean memory cartridge, drag both the Linux Installer "Install Linux" save and the Splinter Cell "LINUX_Profile" save to it, copy them to your Xbox, start the game, select the profile, and it should blip to a black screen for a few secs, and the softmod installer screen should pop up. This actually happened to me my second softmodding. Make sure your splinter cell save is the right type (NTSC or PAL), if still doesn't work, recopy the "SID.Splinter.Cell.v2.0.** Links to Xbox Warez and Torrents **.zip" to Action Replay, etc...
Best of luck
Dark Griff